Hindoo Koosh , (Pers. Hindu Kuh, Indian mountain), a range of mountains in central Asia, which was known to the ancients as the Indian Caucasus. Although the name more strictly belongs to the lofty snow-clad summit, upward of 20,000 ft. in height, which rises directly N. of the Cabool valley, it is applied to the entire mountain tract extending from the southern portion of the elevated table land of Pamir, in about lat. 37° N., Ion. 73° E., to the region near Ion. 68° immediately W. of the city of Cabool. It separates the Punjaub and Afghanistan on the south from Badakhshan and Koon-dooz on the north. The least elevation of the range relative to the surrounding country appears to be on the plateau which forms its eastern extremity, where it is approached by the Karakorum mountains. The absolute height of the eastern portion of the Hindoo Koosh, however, is very great, the Nuksan pass, between Chitral on the south and Wakhan on the north, being estimated to be 17,000 ft. above the level of the sea. There are glaciers in this region. The range decreases in elevation as it stretches westward. Those peaks whose heights have been determined are upward of 20,000 ft. in altitude.

The section which has been most thoroughly explored lies between the 70th and 68th meridians, from the Khawak pass on the east to the Hadjiyak passes on the west. It is described as an unpierced watershed, closely corresponding to the line of highest peaks, and crossed by 19 passes, none less than 12,000 ft. high. The Khawak pass, 13,-500 ft., is supposed to be that which was traversed by Tamerlane on his way to the conquest of India, and by Alexander the Great on his return from Bactria. The three Hadjiyak passes, about 13,000 ft., lead from the head of the Cabool valley to Bamian in the basin of the Oxus, and are usually regarded as the limit of the Hindoo Koosh on the west, the name Koh-i-baba being applied to the western extension of the range. The Cabool and Hel-mund rivers rise on the southern slope of the watershed, and from the northern side flow several important tributaries of the Oxus. The Hindoo Koosh is characterized by excessive aridity and a remarkable absence of forests.